A network is a system that allows communication between members of the network. Wireless networks allow such communications without the physical constraints of cables and connectors. Recently, wireless local area networks (a local area network is a computer network covering a local area such as an office or a home) with ranges of about 100 meters or so have become popular. Wireless local area networks are generally tailored for use by computers, and as a consequence such networks provide fairly sophisticated protocols for establishing and maintaining communication links. Such networks, while useful, may be unsuitably complex and too power-hungry for electronic devices of the future.
A wireless personal area network is a network with a more limited range of about 10 meters or so. With the more limited range, such networks may have fewer members and require less power than local area networks. The IEEE (Institute of Electrical and Electronics Engineers) is developing a standard for wireless personal area networks. The IEEE 802.15.3 standard specifies a wireless personal area medium access control (MAC) protocol and a physical (PHY) layer that may offer low-power and low-cost communications with a data rate comparable to that of a wireless local area network. The standard coins the term “piconet” for a wireless personal area network having an ad hoc topology of devices coordinated by a piconet coordinator (PNC). Piconets form, reform, and abate spontaneously as various electronic devices enter and leave each other's proximity. Piconets may be characterized by their limited temporal and spatial extent. Physically adjacent devices may group themselves into multiple piconets running simultaneously.
The IEEE 802.15.3a task group is developing a new PHY layer operating in an ultra wide band (UWB) and providing very high data rates (in the order of 100 Mbps). Currently this PHY layer is based on frequency hopping (FH) orthogonal frequency division multiplexing (OFDM), whereby the OFDM symbols of a data packet are successively sent in a pre-ordered sequence of frequency bands comprising all or part of the UWB frequency range. There may be a variety of such sequences, which are referred to as frequency hopping (FH) sequences herein but may be given other terms in the final standard or the technical literature. The frequency hopping nature of the PHY makes simultaneously operating piconets susceptible to mutual interference. The draft IEEE standard proposes that each PNC selects an FH sequence for use by the devices in its piconet for data transmission. However, this creates a significant likelihood of repeated collisions between adjacent piconets that happened to have chosen the same FH sequence. Accordingly, a randomization mechanism for avoiding persistent interference and hence improving network performance (in terms of user throughput and delay) is desired for the robust operation of ad hoc piconets and other wireless personal area networks in general.